System and method for compression of fluids

ABSTRACT

A fluid compressor for compressing fluids and a method for operating the same are provided. The fluid compressor includes a compression chamber with an inlet for the fluid and an outlet for compressed fluid. The fluid compressor further includes a piston disposed within the compression chamber. The fluid compressor includes a driving system that includes piezoelectric actuator configured to cause displacement of the piston in the compression chamber. The driving system further includes an amplifying element that is coupled to the piezoelectric actuator in the direction of the movement of the piston to enhance the displacement of the piston caused by the piezoelectric actuator. One end of the amplifying element is fixed to a base of the fluid compressor and the piezoelectric actuator is disposed between the amplifying element and the piston.

BACKGROUND OF THE INVENTION

Embodiments of the present invention are related generally to the field of cooling systems and, more particularly, to a system and method for compression of fluids.

Compressors are typically used in systems and appliances that require fluids to be compressed and obtain high pressure. Such a need is felt in systems that follow a thermodynamic refrigeration cycle, for example, but not limited to, refrigerators, air conditioners, automotive cooling systems, and power plant cooling systems. Compressors are employed in such systems to compress the coolant and maintain a desired temperature in the system.

Compressors commonly utilize a piston that compresses fluids entering a hollow cylinder, called compression chamber, in the compressor body. The piston moves linearly back and forth to compress the fluid to create the high pressure fluid required to carry out the cooling operations in the system. The piston is displaced from an original position and kept in motion whenever the requirement for compressing fluids arises. Several configurations exist where the piston is set in motion to ensure fluids are compressed.

In an exemplary configuration, piezoelectric materials have been used as actuators to initiate displacement of pistons in the compressors. The piezoelectric material is provided with an excitation signal that causes the material to expand or contract. Generally, the piezoelectric material is coupled with the piston in such a way that the piston is displaced back and forth in the compression chamber, when the piezoelectric material experiences a change in shape and/or form.

Although the piezoelectric material causes displacement that may be desirable to compress fluids, the amount of displacement is dependent on several parameters including an excitation signal provided to the material. For high pressure requirements in a compression cycle in systems that require intensive cooling at a fast rate, a significant amount of energy is consumed by the excitation signal to be provided to the piezoelectric material. Moreover, piezoelectric material alone, even when provided with sufficient excitation signal, cannot provide both force and displacement to achieve the high pressure requirements at a fast rate.

Accordingly, there is a need for an improved system and method that provides for energy efficiency in driving the piston in the compression chamber of the fluid compressor.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with an embodiment of the invention, a system for controlling temperature of an enclosed space is provided. The system includes a fluid compressor to increase pressure of a coolant fluid. The fluid compressor includes a compression chamber having an inlet for the coolant fluid and an outlet for the compressed coolant fluid. Further, the fluid compressor includes a piston disposed within the compression chamber. The piston within the compression chamber is displaced using a driving system. The driving system includes a piezoelectric actuator coupled to the piston to cause lateral displacement of the piston in the compression chamber in response to an excitation signal. The driving system also includes an amplifying element operatively coupled to the piezoelectric actuator in the direction of the movement of the piston to enhance the displacement of the piston caused by the piezoelectric actuator. One end of the amplifying element is fixed to a base of the fluid compressor and the piezoelectric actuator is disposed between the amplifying element and the piston. Furthermore, the system to control temperature includes a condenser operatively coupled to the fluid compressor, to remove a portion of the heat contained in the compressed high temperature coolant fluid. The system also includes an expansion valve to reduce pressure of the compressed coolant fluid entering from the condenser and further reduce the temperature of the compressed coolant fluid. An evaporator to control temperature of the enclosed space by drawing heat from the enclosed space through the coolant fluid from the expansion valve is also included in the system.

In accordance with another embodiment of the invention, a system to compress fluids is provided. The system includes a driving system to displace a piston back and forth in a compression chamber. The driving system includes a piezoelectric actuator that causes a displacement of the piston in the compression chamber. The piston is disposed on top of the piezoelectric actuator. Further, the driving system includes an amplifying element that is coupled to the piezoelectric actuator to enhance the displacement caused by the piezoelectric actuator. The amplifying element is disposed in such a way that the piezoelectric actuator is placed on a top end of the amplifying element and an opposite end of the amplifying element is mechanically coupled with a base of the fluid compressor.

In accordance with another embodiment of the invention, a method for compressing fluids in a fluid compressor is provided. The method for compressing fluid includes displacing a piezoelectric actuator from its initial position with an excitation signal. The piezoelectric actuator is disposed below a piston of the fluid compressor that is configured to displace back and forth in a compression chamber of the fluid compressor. Further, the method includes amplifying the displacement of the piston by a degree of at least seven using an amplifying element. The amplifying element is disposed in such a way that the piezoelectric actuator is disposed on a top end of the amplifying element and an opposite end of the amplifying element is mechanically coupled with a base of the fluid compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will become apparent from the following detailed description of the invention when read with the accompanying drawings in which:

FIG. 1 is a schematic illustration of a system to control temperature of an enclosed space embodying certain aspects of the present invention;

FIG. 2 is a block diagram representation of the fluid compressor embodying aspects of the present invention;

FIG. 3 is a flow chart representing an exemplary method of operating a fluid compressor according to an embodiment of the present invention;

FIG. 4 is a block diagram representation of a feedback controller to control an excitation signal provided to a piezoelectric actuator according to one embodiment of the present invention;

FIG. 5 illustrates graph comparing performances of one embodiment of the present invention and another configuration of a fluid compressor, with respect to frequency of the fluid compressor as a function of amplifying element stiffness; and

FIG. 6 illustrates a graph comparing performance of an embodiment of the present invention and another configuration of a fluid compressor, with respect to stroke pressure as a function of amplifying element stiffness.

DETAILED DESCRIPTION OF THE INVENTION

While embodiments of the present invention have been shown and described herein, such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.

As discussed in detail below, embodiments of the invention include a driving system for compression of fluids. Aspects of the present technique reduce energy consumption of compressors used to compress fluids. The system further provides for displacement of a piston in the fluid compressor at resonant frequency, thus achieving compression at a fast and efficient rate. The system as per the present technique includes a piezoelectric actuator and an amplifying element. The piezoelectric actuator is coupled to the piston to cause lateral displacement of the piston in the compression chamber in response to an excitation signal. The system further includes an amplifying element operatively coupled to the piezoelectric actuator in the direction of the movement of the piston to enhance the displacement of the piston caused by the piezoelectric actuator. The amplifying element is disposed in such a way that one end of the amplifying element is fixed to a base of the fluid compressor and the piezoelectric actuator is disposed between the amplifying element and the piston. The present technique is described in greater detail in the foregoing paragraphs with the help of accompanied drawings.

FIG. 1 is a schematic illustration of a system 100 for controlling temperature of an enclosed space embodying aspects of the present invention. The system 100 may be used to control temperatures of a storage enclosure, a room or similar spaces that require temperature control. The system 100 includes a fluid compressor 102, a condenser 104, an expansion valve 106, an evaporator 108, and a fan 110. The fluid compressor 102 increases temperature of a coolant fluid by compressing the coolant fluid. The fluid compressor 102 includes a compression chamber, a piston, and a driving system. The driving system of the fluid compressor 102 further includes a piezoelectric actuator and an amplifying element (not shown). The details of the fluid compressor 102 are explained in FIG. 2. The high temperature compressed coolant fluid flows from the fluid compressor 102 to the condenser 104. The condenser 104 reduces temperature of the high temperature compressed coolant fluid. Furthermore, the coolant fluid leaving the condenser 104 enters the expansion valve 106. At the expansion valve 106, the coolant fluid undergoes an abrupt reduction in pressure. The reduction in pressure leads to further reduction of temperature in the coolant fluid. The coolant fluid at reduced temperature enters the evaporator 108 from the expansion valve 106. The evaporator 108 is configured to draw heat from the enclosed space using the coolant fluid at reduced temperature. Warm air 112 from the atmosphere passes through the coolant fluid in the evaporator 108 and cold air 114 enters the enclosed space thereby drawing heat from the enclosed space. Further, the coolant fluid that gets heated due to extracting heat from the enclosed space is passed to the fluid compressor 102 to continue with the cycle for controlling temperature of the enclosed space.

In the illustrated embodiment, the system 100 includes a fan 110 that blows the warm air 112 from the atmosphere on the coolant liquid in the evaporator 108. Further, according to certain embodiments of the present invention, the condenser 104 includes coiled tubes 118 to carry the compressed coolant fluid. According to another embodiment of the present invention, the evaporator 108 also includes coiled tubes 116 to carry the coolant fluid in and out of the enclosed space.

In another embodiment, the system 100 includes an excitation sub-system (not shown) that provides an excitation signal to the piezoelectric actuator in the fluid compressor 102. The system 100 also includes a feedback controller to control at least one of frequency and amplitude of the excitation signal provided to the piezoelectric actuator. The feedback controller includes at least one of a pressure sensor, a temperature sensor, and a stroke sensor that sense at least one of pressure of the coolant fluid in the compression chamber, temperature of the coolant fluid in the compression chamber, and a stroke of the piston within the compression chamber respectively. The feedback controller provides a feedback to the excitation sub-system based on the information obtained from at least one of the sensors to provide excitation signal that displaces the piezoelectric actuator appropriately to achieve efficient performance.

FIG. 2 is a block diagram representation of the fluid compressor 102 in FIG. 1. The fluid compressor 102 includes a compression chamber 202, a piston 204, an inlet 210, an outlet 212, and a driving system according to one embodiment of the present invention. The driving system includes a piezoelectric actuator 206, and an amplifying element 208. The piezoelectric actuator 206 is configured to cause lateral back and forth displacement of the piston 204 in the compression chamber 202 in response to an excitation signal. Further, the piezoelectric actuator 206 is operatively coupled to the amplifying element 208. The amplifying element 208 is configured to enhance the displacement of the piston caused by the piezoelectric actuator 206. The amplifying element 208 is disposed in the direction of the movement of the piston. Furthermore, one end of the amplifying element 208 fixed to a base 214 of the fluid compressor 102, and the amplifying element 208 is disposed in such a way that the piezoelectric actuator 206 is disposed between the amplifying element 208 and the piston 204.

According to one embodiment of the present invention, the piezoelectric actuator 206 is fixed with the amplifying element 208 using at least one of nuts, bolts, rivets, or any known adhesive material. According to another embodiment of the present invention, the amplifying element 208 is fixed with the base 214 of the fluid compressor 102 using at least one of nuts, bolts, rivets, or any known adhesive material.

In one embodiment, the fluid compressor 102 includes an excitation sub-system configured to provide the excitation signal to the piezoelectric actuator 206. The excitation signal provided by the excitation sub-system is an electric signal that causes a displacement in the piezoelectric actuators. When the excitation signal is transmitted to the piezoelectric actuator 206, the piezoelectric actuator 206 expands or contracts depending on a phase of the excitation signal and causes the piston 204 to move. The movement of the piezoelectric actuator 206 causes the amplifying element 208 to stretch or expand. The change in shape of the amplifying element 208 caused by the piezoelectric actuator 206 causes an enhancement in the displacement of the piston 204. The displaced piston 204 then causes the fluid entering the compression chamber 202 through the inlet 210 to compress. The compressed fluid finally exits the compression chamber 202 through the outlet 212 and is supplied to a system utilizing the fluid compressor 102. According to one embodiment of the present invention, the displacement of the piston 204 is enhanced when the aforementioned operation occurs at resonance. To achieve resonance, the fluid compressor 102 has to be provided excitation signal that has a frequency close to a resonant frequency of the fluid compressor 102. The resonant frequency of the fluid compressor 102 is typically dependent on operating conditions, fluid pressure, and fluid temperature. In another embodiment, the fluid compressor 102 includes a feedback controller coupled to the excitation sub-system to ensure that the fluid compressor 102 operates in a resonant frequency with change in the operating conditions of the fluid compressor 102. The feedback controller is described in greater detail in conjunction with FIG. 4 of this application.

In yet another embodiment, the amplifying element 208 is a coiled spring. The coiled spring has a spring stiffness associated with it, which signifies an amount of change in shape the coiled spring can accommodate. The amount of displacement enhanced by the amplified element 108 varies according to, among other factors, the spring stiffness. When a coiled spring is used as an amplifying element, it is placed in such a way that it is parallel to the direction of the movement of the piston. According to another embodiment of the present technique, the amplifying element 208 is a pre-buckled beam.

The piezoelectric actuator 206, according to one embodiment of the present technique, is a piezoelectric stack actuator. Piezoelectric stack actuators are commercially available in the market and are constructed using piezoelectric materials that convert applied electrical energy to mechanical energy and cause movement. Some examples of commercially available piezoelectric stack actuators include, but are not limited to, Piezomechanik GmBH manufactured PSt/150/14 . . . VS20 series piezoelectric stack actuators, PSt/150/20 . . . VS25 series actuators, PSt/150/7 . . . VS12 series actuators, and other similar piezoelectric stack actuators manufactured by other actuator manufacturers like Noliac®, and CEDRAT Technologies. The piezoelectric actuator 206, according to another embodiment of the present technique, is an amplified piezoelectric actuator that is commercially available in the market. Examples of Amplified piezoelectric actuators include, but are not limited to, APA®, XL series manufactured by CEDRAT Technologies. Alternatively, any piezoelectric material that converts electrical energy to mechanical energy, like Quartz, Topaz, Langasite, Sodium Tungstate, and that can be used to construct a stack of piezoelectric actuator can be used in the fluid compressor 102 as described in the present technique.

In yet another embodiment, the amplifying element 208 and the piezoelectric actuator 206 are selected based on a set of requirements that include, but are not limited to, degree of compression expected, volume of fluid in the compression chamber 202 per cycle, and time taken by the fluid compressor 102 to compress the fluid. In certain situations, a plurality of piezoelectric actuators along with plurality of amplifying elements can be stacked in parallel to cause displacement of the piston in the compression chamber 202.

FIG. 3 is a flow chart representing an exemplary method for operating a fluid compressor according to an embodiment of the present invention. The method, as disclosed, is intended to be practiced on the fluid compressor 102 described in FIG. 2. Elements from FIG. 2 have been denoted with the same reference number for the sake of clarity. The method includes, at step 302, monitoring at least one of fluid pressure or fluid temperature in the compression chamber 202 of the fluid compressor 102. The fluid compressor 102, as described in conjunction with FIG. 2 includes piston 204, and a driving system that includes a piezoelectric actuator 206 and an amplifying element 208. The piezoelectric actuator 206 is configured to cause lateral displacement of the piston 204 back and forth in the compression chamber 202 by being disposed below the piston 204. The amplifying element 208 enhances the displacement caused by the piezoelectric actuator 206 by at least 7 since the amplifying element 208 is disposed in such a way that the piezoelectric actuator 206 is between the piston 204 and the amplifying element 208. Further, one end of the amplifying element 208 is coupled to a base 214 of the fluid compressor 102. Further, the method includes the step 304 of comparing the monitored value of fluid pressure or fluid temperature and a reference value of the fluid pressure or fluid temperature, respectively. The reference value of the fluid pressure or fluid temperature is indicative of the fluid compressor working at a resonant frequency. Furthermore, at step 306 an excitation signal to the piezoelectric actuator 206 is provided based on a comparison.

The monitored fluid pressure and fluid temperature of the fluid in the compression chamber 202 are analyzed to determine a change in frequency or amplitude of the excitation signal provided to the piezoelectric actuator 206 in such a way that the piston 204 provides maximum strokes and/or the driving system operates in a frequency that is a resonant frequency of the piezoelectric actuator 206.

FIG. 4 is a block diagram representation of a feedback controller 400 to control an excitation signal provided to the piezoelectric actuator 206 according to one embodiment of the present invention. The feedback controller 400 is used to control the excitation signal provided by excitation sub-system 402 to the piezoelectric actuator 206. The feedback controller 400 includes at least one sensor 404, a filter 406, a Phase-Locked Loop (PLL) detector 408, a voltage converter 410, and a processor 412.

An output of the sensor 404 is used to determine at least one of fluid pressure, fluid temperature, and a piston stroke. The output of the sensor 404 is then split in two separate signals using a filter 406. One branch of the output of the sensor 404 is used to compute an amplitude of the displacement of the piston 204 in the compression chamber 202 by first converting the signal to a DC voltage signal through the converter 410. The second branch from the sensor 404 is fed to the PLL detector 408 to determine a frequency at which the piston 204 is being displaced in the compression chamber 202. The processor 412 determines a change that is required in an amplitude and/or frequency of the excitation signal provided by the excitation sub-system 402. The processor 412 is further configured to control the excitation subsystem in such a way that the excitation signal makes the piston 204 displace at resonant frequency.

FIG. 5 illustrates graph comparing performances of one embodiment of the present invention and another configuration of a fluid compressor, with respect to frequency of the fluid compressor as a function of amplifying element stiffness. In the graph illustrated in FIG. 5, the Y axis 502 represents frequency in Hertz (Hz) and the X axis 504 represents amplifying element stiffness in Newton/meter (N/m). Furthermore, the line 506 represents results for a configuration where a piezoelectric actuator is coupled with a base of the compression chamber, and an amplifying element is disposed between the piezoelectric actuator and the fluid compressor's piston, whereas the line 508 represents results obtained by usage of the fluid compressor as described in the present technique. A piston of 150 grams, a piezoelectric actuator of mass 37.7 grams and stiffness constant of 4×106 N/m was used. The fluid pressure in the compression chamber was maintained at 1×106 Pa. It can be seen from FIG. 5 that the frequency at which configuration represented by line 508 operates for different amplifying element stiffness is lesser than the frequency at which the configuration represented by line 506 operates.

FIG. 6 illustrates a graph comparing performance of an embodiment of the present invention and another configuration of a fluid compressor, with respect to stroke pressure as a function of amplifying element stiffness. In the graph illustrated in FIG. 6 the Y axis 602 represents stroke measured in meters (m) and X axis 604 represents amplifying element stiffness measured in Newton/meter (N/m). Further, the line 606 represents results obtained by usage of the fluid compressor as described in the present technique, whereas the line 608 represents results for a configuration where a piezoelectric actuator is coupled with a base of the compression chamber, and an amplifying element is disposed between the piezoelectric actuator and the fluid compressor's piston. A piston of 150 grams, a piezoelectric actuator of mass 37.7 grams and stiffness constant of 4×106 N/m was used. The fluid pressure in the compression chamber was maintained at 1×106 Pa. It can be seen from the results obtained from the experimental tests of the two configurations that the configuration as per the embodiment of the present technique provides for amplified displacement of the fluid compressor's piston.

Further for experimental testing of the fluid compressor 102, a spring with a stiffness of 1.2×105 N/m and a piezoelectric actuator with a constant of 4×106 N/m were selected. The experimental set-up results were compared against a performance of a fluid compressor using only the piezoelectric actuator with the same constant. It was observed that with varying amplitude of excitation signal; the displacement in the fluid compressor as described in the present technique was greater than displacement achieved by using only the piezoelectric actuator. For example, for a voltage of 40V using only the aforementioned piezoelectric actuator a displacement of 2.9 μm is achieved, whereas using the driving system of the fluid compressor 102 described in the present technique a displacement of 74.5 μm is achieved for a voltage of 40V. Similarly for an excitation signal of 120V usage of only the piezoelectric actuator provides a displacement of 42.7 μm whereas the driving system of the fluid compressor 102 of the present technique provides for a displacement of 326 μm. The degree of displacement amplification observed for various amplifying element stiffness has been observed to be at least 7.0.

As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. The systems and methods illustrated are not limited to the specific embodiments described herein, but rather, components of the system may be utilized independently and separately from other components described herein. Further, steps described in the method may be utilized independently and separately from other steps described herein.

While only certain features of embodiments of the invention have been illustrated and described herein, many modifications and changes will occur by those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as they fall within the true spirit of embodiments of the invention. 

What is claimed is:
 1. A system for controlling temperature of an enclosed space, the system comprising: a fluid compressor to compress a coolant fluid, wherein the fluid compressor comprises: a compression chamber having an inlet for the coolant fluid and an outlet for the compressed coolant fluid; a piston disposed within the compression chamber; a driving system comprising: a piezoelectric actuator coupled to the piston, configured to cause lateral displacement of the piston in the compression chamber in response to an excitation signal; and an amplifying element operatively coupled to the piezoelectric actuator in the direction of the movement of the piston, the amplifying element being configured to enhance the displacement of the piston caused by the piezoelectric actuator, one end of the amplifying element being fixed to a base of the fluid compressor, the piezoelectric actuator being disposed between the amplifying element and the piston; a condenser operatively coupled to the fluid compressor, to remove the heat of the compressed high temperature coolant fluid; an expansion valve to reduce pressure of the compressed coolant fluid entering from the condenser and further reduce temperature of the compressed high temperature coolant fluid; and an evaporator to control temperature of the enclosed space by drawing heat from the enclosed space through the coolant fluid from the expansion valve.
 2. The system as recited in claim 1, further comprising a fan that blows air from the enclosed space across the cooled coolant fluid in the evaporator.
 3. The system as recited in claim 1, wherein the condenser comprises coiled tubes to carry the compressed coolant fluid.
 4. The system as recited in claim 1, further comprising an excitation sub-system to provide the excitation signal to the piezoelectric actuator.
 5. The system as recited in claim 4, further comprising a feedback controller operatively coupled to the excitation sub-system to control at least one of frequency or amplitude of the excitation signal.
 6. The system as recited in claim 5, wherein the feedback controller comprises at least one of a pressure sensor, stroke sensor, and temperature sensor.
 7. A fluid compressor comprising: a compression chamber having an inlet for a fluid to be compressed and an outlet for compressed fluid; a piston disposed within the compression chamber for compressing the fluid; a driving system for the piston comprising, a piezoelectric actuator coupled to the piston, configured to cause lateral displacement of the piston in the compression chamber in response to an excitation signal, and an amplifying element operatively coupled to the piezoelectric actuator in the direction of the movement of the piston, the amplifying element being configured to enhance the displacement of the piston caused by the piezoelectric actuator, one end of the amplifying element being fixed to a base of the fluid compressor, the piezoelectric actuator being disposed between the amplifying element and the piston. a feedback controller to control at least one of frequency and amplitude of the excitation signal provided to the piezoelectric actuator.
 8. The fluid compressor as recited in claim 7, further comprising an excitation sub-system for providing the excitation signal to the piezoelectric actuator to cause the displacement in the piezoelectric actuator.
 9. The fluid compressor as recited in claim 7, wherein the feedback controller comprises at least one of a pressure sensor, a stroke sensor, and a temperature sensor.
 10. The fluid compressor as recited in claim 7, further comprising a driving system comprising a plurality of piezoelectric actuators and a plurality of amplifying elements stacked in parallel to displace the piston back and forth in the compressor chamber.
 11. A driving system comprising: a piezoelectric actuator coupled to a piston of a fluid compressor, configured to cause lateral displacement of the piston in a compression chamber, and an amplifying element operatively coupled to the piezoelectric actuator in the direction of the movement of the piston, the amplifying element being configured to enhance the displacement of the piston caused by the piezoelectric actuator, one end of the amplifying element being fixed to a base of the fluid compressor, the piezoelectric actuator being disposed between the amplifying element and the piston.
 12. The driving system as recited in claim 11, further comprising an excitation sub-system for providing an excitation signal to the piezoelectric actuator to cause the displacement in the piezoelectric actuator.
 13. The driving system as recited in claim 12, further comprising a feedback controller coupled to the excitation sub-system to control at least one of a frequency and an amplitude of the excitation signal provided to the piezoelectric actuator.
 14. The driving system as recited in claim 13, wherein the feedback controller comprises at least one of a pressure sensor, a stroke sensor, and a temperature sensor.
 15. The driving system as recited in claim 11, wherein the amplifying element comprises a coiled spring that is placed in a position parallel to a direction of movement of the piston.
 16. The driving system as recited in claim 11, wherein the amplifying element comprises a pre-buckled beam.
 17. The driving system as recited in claim 11, wherein the piezoelectric actuator comprises a stack actuator.
 18. The driving system as recited in claim 11, wherein the piezoelectric actuator comprises an amplified piezoelectric actuator.
 19. The driving system as recited in claim 11, further comprising a plurality of piezoelectric actuators and a plurality of amplifying elements stacked in parallel to displace the piston back and forth in the compressor chamber.
 20. A method of operating a fluid compressor, the method comprising: monitoring at least one of fluid pressure and fluid temperature in a compression chamber of the fluid compressor, comprising a piston that is laterally displaced back and forth in the compression chamber by a driving system, wherein the driving system comprises: a piezoelectric actuator coupled to the piston, and an amplifying element operatively coupled to the piezoelectric actuator in the direction of the movement of the piston, the amplifying element being configured to enhance the displacement of the piston caused by the piezoelectric actuator, one end of the amplifying element being fixed to a base of the fluid compressor, the piezoelectric actuator being disposed between the amplifying element and the piston; comparing at least one of monitored fluid pressure and fluid temperature with a reference value; and providing an excitation signal to the piezoelectric actuator based on the comparison result.
 21. The method as recited in claim 20, further comprising disposing a plurality of piezoelectric actuators with a plurality of amplifying elements, in a position parallel to the piston of the fluid compressor. 